Cleaning and liquid contact with solids – Processes – Hollow work – internal surface treatment
Reexamination Certificate
2000-07-13
2003-05-13
Delcotto, Gregory (Department: 1751)
Cleaning and liquid contact with solids
Processes
Hollow work, internal surface treatment
C134S021000, C134S039000, C134S040000, C252S003000
Reexamination Certificate
active
06561200
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method for generating a foam from a liquid phase and a gas phase, a method for placing a foam in circulation in an installation, and a method for cleaning an installation by placing a foam in circulation.
The invention also relates to a system for generating a foam and to a system for generating and placing a foam in circulation in an installation.
The method of the invention may be of use for example in a method for cleaning and/or decontaminating an installation by means of a foam. Liquid phase cleaning and/or decontaminating methods for a large volume installation, having for example a complex inner geometry, generate considerable volumes of waste. The use of a foam, containing one or more cleaning and/or decontaminating agents brings a significant reduction in the volumes of waste generated. The cleaning and or decontamination of an installation is made by injection of the foam inside the installation to be cleaned and/or decontaminated, and at times by placing the foam in circulation within these installations.
The method of the invention is particularly advantageous for cleaning and/or decontaminating installations operating under low pressure such as a pneumatic carrier network for samples intended for analysis, a ventilation circuit or pipes which have undergone radioactive contamination.
PRIOR ART
Foam generation is generally conducted by mechanical shaking of a liquid, by sudden depressurising of a gas solubilized in a liquid, or by injection of gas and liquid under pressure at the inlet of a static porous medium.
For example patent application EP-A-0 526 305 describes firstly a method for preparing a foam consisting of causing a gas under pressure to pass through a sintered plate in the presence of a solution, the solution and the gas being suitable to form a foam.
The document previously cited also describes a method for cleaning an installation in which the foam is propelled into the installation by the pressure of the gas used to generate the foam. The flow rate of the gas and liquid are set so as to generate foam on entering the installation, irrespective of the characteristics of said installation to be cleaned. The method of preparing a foam and for cleaning an installation described in this document are not appropriate for cleaning sensitive installations, in particular installations for which a pressure greater than atmospheric pressure is prohibited.
It is therefore necessary to put forward a system for generating and placing a foam in circulation which operates at pressures of atmospheric pressure or less.
DISCLOSURE OF THE INVENTION
The purpose of the present invention is to provide a method for generating a foam from a liquid phase and from a gas phase with which homogeneous foam can be generated having few or no air pockets.
The method of the invention is characterised in that it comprises a step consisting of generating the foam by aspiration of the liquid phase and the gas phase through a porous lining.
The principle of the method of the invention consists of no longer injecting liquid and gas phases under pressure through the porous lining, but of draining them through the pores or interstices of the lining by setting up constant low pressure downstream from this lining.
The gas phase and the liquid phase are aspirated simultaneously through the lining under the effect of low pressure. The porous lining therefore acts as a contacter between the gas phase and the liquid phase.
The gas phase-liquid phase mixture is made in the porous lining in which interfaces are created and therefore foam is created. The energy required for this mixture and the creation of interfaces is provided by the flow of the liquid and gas phases in the lining under the effect of low pressure.
In order to obtain a foam of constant quality when it leaves the lining, various variables need to be controlled which come into play during the generation method described above. These variables are the chemical composition of the liquid phase, also called foaming solution, the flow rate of the liquid phase arriving in contact with the porous lining, the flow rate of the gas phase drawn by aspiration, the geometry of the porous lining placed in a chamber, and the geometry of said chamber.
The chemical composition of the foaming solution is chosen in relation to the intended use of the generated foam. The foam may, for example, be a cleaning and/or decontaminating foam for an installation, and/or a scouring foam, a rinsing foam, a foam intended to apply a film having surfactant or bactericidal properties for example.
The quality of the foam may be determined for example by a lifetime, a moisture content, or its expansion. The lifetime of a foam may be defined as the time required for total conversion of a given volume of foam into liquid and gas. The moisture content of a foam may be defined as the ratio between the liquid phase volume and foam volume. Expansion F of a foam is defined, under normal temperature and pressure conditions by the following ratio (1):
F
=
V
gas
+
V
liquid
V
liquid
=
V
foam
V
liquid
in which:
F=expansion in units of expansion
V
gas
=the volume of the gas phase in the foam
V
liquid
=the volume of the liquid phase in the foam
V
foam
=the volume of foam.
A foam having constant quality will have constant expansion. Generally, the foams prepared with the methods of the prior art have an expansion in the order of 10 to 15. Expansion also provides a magnitude of the amount of decrease in the volume of generated liquid waste for example, when the foam is used to clean an installation.
Expansion also makes it possible to assess the quantity of air pockets present in the foam, and therefore to assess the quality of this foam.
If the foam is intended to carry out cleaning and/or decontamination and/or scouring, according to the method of the invention, the liquid phase may also comprise at least one foaming surfactant conventionally used to generate a foam, at least one foam stabilising or destabilising agent with which it is possible to modify the lifetime of the foam or its moisture content, and/or at least one cleaning agent and/or at least one decontaminating agent and/or at least one scouring agent for an installation.
If the foam is intended to carry out rinsing of an installation, the liquid phase may be an aqueous solution of at least one surfactant agent and of at least one foam destabilising agent.
In a foam composition that can be used to implement the method of the invention, the constituents of the liquid phase, in particular the foam destabilising agent, and their quantity are chosen such as to obtain a foam lifetime of 15 to 30 minutes and a moisture content of 2 to 20%.
Examples of appropriate liquid phases to implement the method of the invention are described in EP-A-0 526 305.
The destabilising agent may be an organic compound which destabilises the foam by acting on dynamic surface tension, for example an alcohol preferably having a boiling point slightly higher than that of water, for example a boiling point of 110° C. to 130° C. Preferably a C5 to C6 secondary alcohol is used, such as pentanol-2.
Generally the quantity of destabilisation agents represents from 0.2 to 1% by weight of the liquid phase.
In the liquid phase of the foam, the decontamination reagent may be made up of reagents routinely used in wet process decontamination methods. If the objects to be decontaminated are in metal, particular use is made of reagents made up of inorganic or organic acids or bases. As an example of acid reagents, mention may be made of hydrochloric acid, nitric acid, sulphuric acid and phosphoric acid which may be used alone or in combination. It is also possible to use organic reagents such as citric or oxalic acids.
As an example of basic reagents NAOH, KOH and their mixtures may be cited, to which oxidants for example may be added, such as H
2
O
2
or the permanganate ion.
In the case of acid reagents, their concentration in the liquid phase may range for example up to 10 mol.1
−1
;
Faury Maria
Fournel Bruno
Le Samedy Jean-Marie
Burns Doane Swecker & Mathis L.L.P.
Commissariat a l'Energie Atomique
Delcotto Gregory
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